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DIY: Foglight Wiring Harness Install (MKIV)

This guide is for installing a headlight foglight wiring harness into a car that does not come with them stock. This procedure will only be necessary after upgrading to OEM or aftermarket headlights with built-in fogs.

Note - This install was completed on a MKIV Jetta. Although I can't be entirely certain, I believe the instructions would be identical for an MKIV Golf/GTI.

1. Begin by unhooking the battery. Use the 10mm socket and ratchet to loosen the bolt on the negative terminal. Pull up on the connector to remove it from the post. Tuck it off to the side so it doesn’t touch the terminal.

2. Start by laying the harness out over the engine bay to see where to run the wires. There are 5 wires that need to be hooked up in total; one wire will go to your driver’s side headlight, one to the passenger side headlight, one to the positive terminal on your battery, one to the negative terminal (or equivalent ground), and the last goes through the firewall and into the euroswitch. We’ll worry about that later though.

3. Begin by removing the plastic cover behind the driver’s side headlight. There are 4 Philips screws that hold in the two pieces. Remove them.

4. Gently pull up to remove the covers. Note that the hood release cable goes along the back of one piece and into the other. Be careful not to twist or move the cable too much as the plastic coating gets quite brittle with age, and I’m unsure how badly it may rust if not protected.

5. Grab your flathead screwdriver. Insert the end in the slot connecting the headlight harness to the headlights. Pull gently towards yourself to loosen the connector and pull it off.

6. Look at the back of the headlight wiring harness. Note the little green grommets in the spare locations. Grab a pin or pair of tweezers and pull out the grommet located in the hole marked 2.

7. Now flip the harness over and look inside. You’ll see a purple ring going around the entire centre section. Grab either your flathead screwdriver or a small pin and slide it off to the side (it will only come out one way). This will allow you to plug in the foglight wire.

8. Flip the headlight harness back over and insert the wire into the hole you removed the grommet from. It will click into place.

Note – Some foglight harnesses come with grommets on the wire to keep water and dirt out. If yours didn’t come with one and you’d like it on there, you can drill a hole through the centre of the green grommet you removed and push that over the spade connector.

9. Push the purple ring back into place.

10. Repeat steps 5 through 9 on the passenger side headlight

11. Use the 10mm socket and ratchet to remove the bolts from both the positive and negative terminal connectors (the things that slide over the posts on the battery). Place the red power wire on the positive terminal connector, and the grey or brown ground wire (colour differs depending on harness brand) onto the negative terminal connector. Do not place the negative terminal connecter back on the negative post yet.

12. Its time to start taking apart the interior for the other half of the job. First, remove the headlight switch. To do this, push in on the switch while turning it clockwise to the “On” position. The centre part of the switch will sink in. Turn the switch clockwise a little more. This will retract the little tabs holding it in place. Pull the switch straight out as show in the picture.

13. There are two tabs holding the harness to the switch. Push in on the sides to release the switch. Set the switch somewhere, you won’t need it for a while.

14. Time to start taking apart the interior to run the wire to the euroswitch. Begin with the entire panel on the left side of the dash.

15. Use a flathead screwdriver to pop the spring clips out of place. There are 3 in total (one near the top, one in the middle and one near the bottom). Pull it towards you to remove it.

Note – Some cars have the same soft rubbery coating on this panel as the door handles and trim around the radio and HVAC controls. Be careful not to damage it.

16. To get access to the wire you’re running through the firewall, you’ll have to remove the kick panels to the left and right of the steering wheel as well as the plastic cover underneath. Begin with the left half. Remove the two T20 Torx screws holding it in place. (sorry for posting two pics, didn’t have my wide angle and couldn’t get both screws in the shot)

17. Grab the panel from the side, and pull it straight out. It’s held in by two spring clips near the top.

18. Get back under the dash and remove the T20 Torx screw holding the right side of the kick panel in place.

19. Grab the panel from the bottom and gently pull it straight out. I believe there’s only one clip holding it in at the top, but it’s also mounted against the radio cage and takes a bit of effort to get off.

20. The last piece you need to remove is the plastic cover from the bottom. There’s a spring clip at the front holding it into place, and two large flat white clips holding it in at the back. Pull the whole piece straight out.

21. Now it’s time to route the wire through the firewall. The easiest place is the rubber grommet next to the brake booster. Pull it out by grabbing one side of it with your fingers. It will pop right out. Drill or melt a hole in the grommet and feed the wire through. If you want you can seal it with some high-temp silicone.

Note – Picture below is from a 1.8T. This install was done on a 2.0L which had that grommet occupied by the throttle cable. There is another grommet further down near the clutch pedal that can also be used, but were unable to get the camera down there for a photo.

22. Take the wire you fed through the grommet and route it under the dash across to the headlight harness. Plug the wire into the spot marked “8”. It will click into place if inserted correctly.

23. You’re pretty much done! Put the negative connector back on the terminal post and tighten with the 10mm socket and ratchet. If you haven’t already done so, tighten the bolt on the positive terminal as well to secure the power wire in place.

24. Plug your switch back into the harness and test to make sure everything works before you put your car back together again.

Note – The key must be in the “on” position (or the car turned on) for the foglights to come on. They will not turn on otherwise.

25. If everything worked, start putting everything back together in reverse order:

- Put plastic cover back on bottom of dash; make sure back of cover slides back into white clips
- Reinstall right side of kick panel by pushing back into place, spring clip will click back into place, reinstall single Torx screw in bottom
- Reinstall left side of kick panel by pushing back into place, two spring clips at top will click back into place, reinstall two Torx screws in bottom
- Put fuse cover panel back into place and push spring clips into place
- Reinsert euroswitch into dash; when it place, turn switch counter-clockwise to release tabs and lock switch into place
- Tie-wrap wires in engine bay out of view
- Find a place to mount the harness relay

Note - As with any Do It Yourself guide, proceed at your own risk. I am not responsible for any damage you may do to your car attempting this install.

Special Thanks go to:

- Giver for providing the car for this project, the garage, food and beer
- LuiTuga for doing a majority of the work
- rictuga for BBQ'n the day we did this... mmnnn... burgers....

Pictures?

I know this post is pretty old and no one has posted in forever but is there any way the pictures can be posted back up? I'm stuck on the the rubber grommet next to the brake booster part and I'm curious on where it is. I might be blind but the pictures might help. Thanks!